1. Field of the Invention
The present invention concerns Angptl3 polypeptides as well as methods and means for making and using such protein molecules, and antibodies binding Angptl3 polypeptides.
2. Description of the Related Art
The growth of new blood vessels is a prerequisite during normal physiological processes of embryonic and postnatal development. Such proliferation of new blood vessels from pre-existing capillaries, a process termed angiogenesis, additionally plays a key role in the pathological development of solid tumors, diabetic retinopathies, psoriasis, inflammation and rheumatoid arthritis (Ferrara, Recent Prog. Horm. Res. 55:15-35 (2000), discussion 35-6).
Angiogenesis not only depends on growth factors, such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF), but is also influenced by cell adhesion molecules (CAMs), including integrins. Inactivation of various genes encoding specific adhesion receptors or administration of blocking antibodies in animal models had profound effects on the angiogenic response of endothelial cells (Elicieri and Cheresh, Mol. Med., 4:741-50 (1998)).
The integrin family of cell adhesion proteins is composed of 15α and 8β subunits that are expressed in at least 22 different αβ heterodimeric combinations (Byzova et al., Mol. Cell., 6(4):851-60 (2000)). Among these, at least six (αvβ3, αvβ5, α5β1, α2β1, αvβ1 and α1β1) of the combinations have been implicated in angiogenesis (Hynes and Bader, Thromb. Haemost., 78(1):83-7 (1997); Hynes et al., Braz. J. Med. Biol. Res., 32(5):501-10 (1999)). Integrins facilitate cellular adhesion to and migration on the extracellular matrix proteins found in intercellular spaces and basement membranes.
Integrin αvβ3 is a receptor for a wide variety of extracellular matrix proteins including vitronectin, fibronectin, fibrinogen, laminin, collagen, Van Willebrand factor, osteopontin and a fragment of MMP2 (PEX) among others (for review see Eliceiri and Cheresh, Cancer J. Sci. Am. 6 Suppl 3:S245-9 (2000)). Despite its promiscuous ligand binding behavior, αvβ3 is not widely expressed in adult tissues, is found on some vascular, intestinal and uterine smooth muscle cells (Brem et al., Invest. Opthalmol. Vis. Sci., 35:3466-74 (1994). This receptor is also expressed on certain activated leukocytes, on macrophages and osteoclasts, where plays a crucial role during bone resorption (McHugh, et al, J. Clin. Invest., 105:433-40 (2000)). Most prominently, αvβ3 becomes upregulated on endothelial cells exposed to hypoxia and cytokines such as vascular endothelial growth factor A (VEGF-A) (Suzuma et al., Invest Opthalmol. Vis. Sci. 39:1029-35 (1998); Walton et al., J. Cell. Biochem., 78:674-80 (2000)). In vivo, increased expression of αvβ3 was observed on vascular cells within tumor granulation tissues, during wound healing, macular degeneration and other neovascular diseases. In a variety of in vitro and in vivo models of tumor angiogenesis, blockade of αvβ3 with monoclonal antibodies or ligand antagonists led to blunted blood vessel formation (Brooks et al., Cell 79:1157-64 (1994); Eliceiri and Cheresh, Mol. Med. 4:741-50 (1998)).
While there is a vast number of reports focusing on the mechanism involved in regulation of angiogenesis in pathological conditions such as tumor growth or collateral vessel formation after myocardial ischemia, surprisingly little is known about the role of the angiogenic process during liver regeneration. After partial hepatectomy (PH), both hepatocytes and nonparenchymal cells expressed vascular endothelial growth factor (VEGF) mRNA (Mochida et al. Biochem. Biophys. Res. Commun. 226:176-9 issn: 0006-291x (1996)), implicating that VEGF, by means of inducing angiogenesis, might play a role in liver regeneration. However, neutralizing antisera against VEGF did not alter recovery rates after injury but led to a reduction of proliferating endothelial cells and hepatocytes in this model (Taniguchi et al., J. Histochem. Cytochem. 49:121-30 (2001)). In support of this, the addition of the angiogenesis inhibitor TNP-470 did not impair wound healing after partial hepatectomy, suggesting that TNP470-sensitive angiogenesis is not required during liver regeneration (Tanaka et al., Br. J. Surg., 83(10):1444-7 (1996)).
There is a need for the identification of novel factors which are involved in liver regeneration, and in particular in the process of angiogenesis during liver regeneration.